1. Field of the Invention
The present invention relates to a projection type display apparatus. In particular, the present invention relates to a projection type display apparatus for improving contrast while suppressing a fall in brightness in the projection type display apparatus as a whole.
2. Related Art
As an example of a structure of a projection type display apparatus, a cathode-ray tube (CRT: Cathode Ray Tube) rear projector apparatus will be described with reference to FIGS. 1(A), 1(B), FIG. 2, FIG. 3 and FIG. 4. In addition, the basic structure of the CRT rear projector apparatus is the same as that of a conventional technique and that of a preferred embodiment according to the present invention. Referring to FIGS. 1(A), 1(B), FIG. 2, FIG. 3 and FIG. 4, the structure, operations, etc. of the CRT rear projector apparatus will be described in detail in “Best Mode for Implementing the Invention.”
As shown in FIG. 1(A) a CRT rear projector apparatus 1 includes a CRT video projection unit 10, a reflecting mirror 12, a screen unit 14, and a casing 16. The CRT video projection unit 10, the reflecting mirror 12, and the screen unit 14 are accommodated in the casing 16. As shown in FIG. 1(B), the CRT video projection unit 10 includes a red CRT display apparatus 10R, a green CRT display apparatus 10G, and a blue CRT display apparatus 10B which output monochromatic images respectively.
FIG. 2 representatively shows a schematic cross-sectional structure of the red CRT display apparatus 10R. The red CRT display apparatus 10R includes a CRT display tube 101, a coupler 103, a lens unit 104, and a deflecting yoke 102 which is provided around the perimeter of a neck portion of the CRT display tube 101 and deflects an electron beam. An electron gun (not shown), a fluorescent material 101a, etc. are provided inside the CRT display tube 101, and a face glass 105 is provided in the front. The coupler 103 is a unit which combines the CRT display tube 101 and the lens unit 104. Since the CRT display tube 101 reaches a considerably high temperature, cooling fluid 103a is accommodated. The image outputted from the CRT display tube 101 penetrates the coupler 103, and is magnified with a plurality of lenses in the lens unit 104, then projected on the reflecting mirror 12 which is located on a front surface of the red CRT display apparatus 10R.
The respective monochrome images outputted from the red CRT display apparatus 10R, the green CRT display apparatus 10G, and the blue CRT display apparatus 10B are directed to the reflecting mirror 12, reflected in the reflecting mirror 12, and then projected on the screen unit 14, so as to be synthesized into a color image on this screen unit 14.
As illustrated in FIG. 3 the screen unit 14 includes a Fresnel lens 145, a lenticular lens 143, and a screen 141 which are disposed along the direction of movement of the images directed from the reflecting mirror 12 to the screen unit 14.
Being reflected in the reflecting mirror 12, the respective monochrome images of red, green, and blue are projected (make an image) on the screen 141 via the Fresnel lens 145 and the lenticular lens 143, so that the respective monochrome images of red, green, and blue are synthesized into a color image. A viewer 20 can see the color image projected on the screen 141.
Generally explaining a display apparatus, it is always a technically big proposition “to make black as black as possible” in order to improve quality of image. Similarly, as for the CRT rear projector apparatus, there is no exception to the fact that “to display black as black as possible” is an important factor to the improvement in quality of image. Thus, as to a variety of conventional display apparatuses, various measures have been taken for the proposition “to display black as black as possible.”
FIG. 4 is a view for illustrating relationships among main light, stray light, and outside light in a color CRT of an image receiving apparatus of a conventional color television set. It is known that since a fluorescent material used for a color CRT is white in principle, a portion which is not excited by an electron beam, that is a black portion in terms of an image, stands out in white when irradiated with the outside light, so that the contrast (=white brightness/black brightness) of display may be reduced or the contrast of display is lost.
As for conventional color television receivers, in order to improve the fall in contrast of display, the face glass of the color CRT etc. is generally tinted so as to reduce image light (attenuation) (see Japanese Laid-open Patent Application No. H06-139968, Japanese Laid-open Patent Application No. 2000-324427, for example).
In other words, as will be described hereinafter with reference to FIG. 4, tinting may cause the attenuation of the outside light and the attenuation of the stray light, which improves the contrast.
(1) Attenuation of Outside Light
As illustrated in FIG. 4, the main light from the fluorescent material in the color CRT passes through the tinted face glass once. On the other hand, the outside light passes through it twice, at the time of being incident to the tinted face glass and at the time of leaving the tinted face glass. Therefore, the attenuation of outside light is larger than that of the main light.
(2) Attenuation of Stray Light
As illustrated in FIG. 4, light from a light emission portion of the fluorescent material in the color CRT is reflected in a boundary face of the tinted face glass, so that a fluorescence side of the black portion which should not shine is illuminated, and the black stands out. This light is called stray light. At this time, the number of attenuations of the stray light passing through the tinted face glass is three or more. Further, its angle is oblique and its path is long, so that the attenuation of the stray light is considerably greater than that of the main light. Thus, in the conventional color CRT, using the tinted face glass improves the contrast and contributes to the improvement in quality of image.